The present invention relates to improvements in metal halogen battery systems. More particularly the invention relates to a new zinc-chloride battery system. The invention herein is particularly useful for mobile battery applications, e.g., for electric vehicles.
The electrical energy storage systems of the type referred to herein (e.g., a zinc-chlorine battery system) utilize a halogen hydrate as the source of a halogen component for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal discharge of the storage system. An aqueous electrolyte is employed for replenishing the supply of the halogen component as it becomes reduced at the positive electrode. The electrolyte contains the dissolved ions of the oxidized metal and the reduced halogen and is circulated between the electrode area and a storage area containing halogen hydrate which progressively decomposes during a normal discharge of the electrical energy system, liberating additional elemental halogen to be consumed at the positive electrode. Electrical energy storage systems or battery systems of this type are described in prior patents owned by the same assignee as the present invention such as U.S. Pat. Nos. 3,713,888, 3,993,502, 4,001,036, 4,072,540 and 4,146,680. Such systems are also described in published reports prepared by the assignee herein, such as "Zinc-Chloride Electric Engine Unit for Four Passenger Electric Vehicle" by J. Kiwalle and J. Galloway of Energy Development Associates, and EPRI Report EM-1051 (Parts 1-3) dated April 1979, published by the Electric Power Research Institute. The specific teachings of the aforementioned cited references are incorporated herein by reference.
The basic operation of a zinc-chloride battery system is as follows. In charge, an electrolyte pump delivers aqueous electrolyte to pockets between pairs of porous graphite-chlorine electrodes in a battery stack. The electrolyte passes through the porous chlorine electrodes into a chamber between opposite polarity electrodes, flows up between the electrodes, then flows back into the battery sump. Chlorine gas liberated from porous graphite electrolyte substrates is pumped by a gas pump, and before entering the gas pump, the chlorine is mixed with electrolyte chilled by a chiller unit. The chlorine and chilled electrolyte are mixed in the gas pump, chlorine hydrate forms, and the chlorine hydrate-electrolyte mixture is deposited in the store. In discharge, chlorine is liberated from hydrate by decomposition of chlorine hydrate in the store by injection of warm electrolyte from the sump. On development of the required chlorine gas pressure in the store, the chlorine is injected and mixed with and dissolved in the electrolyte, which is then fed to the porous electrodes in the battery stack. The battery stack is then discharged, wherein electrode dissolution of zinc occurs at the zinc electrode, reduction of the dissolved chlorine occurs at the chlorine electrode, power is available from the battery terminals, and zinc chloride is formed in the electrolyte by reaction of zinc and chlorine to form zinc chloride.
There have been certain weaknesses or disadvantages in prior experimental systems directed towards a metal halogen battery system for mobile applications. For example, power dissipation has occurred in such systems because it was necessary to run the gas pump essentially continuously during discharge. Secondly, the pressure differential between the store and the sump was set by a pressure differential valve, which meant that if the store pressure changed, then sump pressure would follow, whereas sump pressure should normally be kept close to atmospheric pressure.
Accordingly it is the main object of this invention to provide a novel and unique metal halogen battery system for mobile applications. Other objects, features, and advantages of the invention will become apparent from the description herein, from the drawings which show preferred embodiments, and from the appended claims.